// Copyright 2014 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
#define UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_

#include "base/macros.h"
#include "ui/events/gesture_detection/gesture_detection_export.h"
#include "ui/gfx/geometry/point_f.h"
#include "ui/gfx/geometry/size_f.h"
#include "ui/gfx/geometry/vector2d_f.h"

namespace ui {

class MotionEvent;

// Port of SnapScrollController.java from Chromium
// Controls the scroll snapping behavior based on scroll updates.
class GESTURE_DETECTION_EXPORT SnapScrollController {
public:
    SnapScrollController(float snap_bound, const gfx::SizeF& display_size);
    ~SnapScrollController();

    // Sets the snap scroll mode based on the event type.
    void SetSnapScrollMode(const MotionEvent& event,
        bool is_scale_gesture_detection_in_progress);

    // Updates the snap scroll mode based on the given X and Y distance to be
    // moved on scroll.  If the scroll update is above a threshold, the snapping
    // behavior is reset.
    void UpdateSnapScrollMode(float distance_x, float distance_y);

    bool IsSnapVertical() const;
    bool IsSnapHorizontal() const;
    bool IsSnappingScrolls() const;

private:
    enum SnapMode { SNAP_NONE,
        SNAP_PENDING,
        SNAP_HORIZ,
        SNAP_VERT };

    const float snap_bound_;
    const float channel_distance_;
    SnapMode mode_;
    gfx::PointF down_position_;
    gfx::Vector2dF accumulated_distance_;

    DISALLOW_COPY_AND_ASSIGN(SnapScrollController);
};

} // namespace ui

#endif // UI_EVENTS_GESTURE_DETECTION_SNAP_SCROLL_CONTROLLER_H_
